The scenarios of GEMM for u/int8 data
Recently, I optimized the kernel of GEMM for int8 data. I found that there was no good solution to do in by the use of the present vector ISA.
The mainly difficult I meet is: The accumulator is 32bits, it needs wide 4 times(vqmacc or vwmul + vwmacc or vwmul + vwadd), which makes the registers are not enough to use.
There are 2 different ways I used to optimize it by he present vector ISA.
1. vdot.vv+vredsum.vs (the tail process is so complex)
2. vwmul + vwredsum.vs (vwredsum.vs used in the for loop)
For solving this, I come up with a new instruction, call vwredsum.vs(new)
Unlike the old vwredsum.vs, the result is put at the first element, the new one can put the result in any position by index. It can be used like this: vwredsum.vs v2, v1, v1, #2
But they are all not good enough. Does someone have better solution?
On 2020-12-11 3:34 a.m., Linjie Yu wrote:
Can we see the git of your work?
Does this mean the 32 vector registers are not enough,
or that the number of elements for the given input vector length
are not enough?
Note vdot.vv is experimental. It is not planned for the v1.0 ratification proposal.
With a "temporary working vector" this new instruction is a combination of the old with any "insert scalar into element" instruction [such as vrgather.vv splatt with mask ].
I would be happy to look at your current work to make suggestions if you could direct me to the code.
Linjie Yu <linjie.ylj@...> 於 2020年12月11日 週五 下午4:34寫道：
Have you consider to use fraction LMUL?